Scientists discover carbon ‘fingerprint’ in tree rings

A recently published study describes a way to more accurately measure the CO2 uptake of trees over their entire lifetimes.

Using nuclear magnetic resonance (NMR), scientists discovered isotopic signals that correspond to specific metabolic processes and allow a deeper understanding of how a tree uses C02 throughout its life. They found that trees of the same species have similarities in these signals.

The researchers write that their results could be used to figure out the responses of tree species to environmental changes as well as aid forest management and climate modeling.

As they grow, trees and other plants take carbon dioxide (CO2) out of the atmosphere and, through photosynthesis, use it to build their tissues by converting it to a type of sugar called glucose. This process plays a critical role in our planet’s food systems and, increasingly, in international plans to stymie climate change such as the Paris Agreement. In part by planting more forests, governments hope to take enough excess CO2 out of the atmosphere to keep global warming under 2 degrees Celsius in the coming century and thereby stave off its worst repercussions.

Yet, exactly how much carbon a tree is capable of sequestering has remained something of a mystery. Until now, that is. A study published recently in Nature’s open-access journal Scientific Reports describes a way to measure CO2 uptake of trees over their entire lifetimes. This, its authors say, could help shed light on how forest carbon uptake may respond to a changing climate and help decision-makers more effectively plan for it.

Researchers at institutions in Sweden, Switzerland and the U.S. used nuclear magnetic resonance (NMR) to measure the proportions of different types of carbon atoms called isotopes at different locations in the glucose molecules that make up cellulose – which is the technical name for the woody pulp in a tree’s trunk. When they used this technique to examine the cellulose of specific rings in trunk cross-sections, they discovered several distinct “signals” of carbon 12 (C12) and carbon 13 (C13) isotopes that appeared at certain points during the trees’ growth.

Black pine (Pinus nigra) was one of the tree species used in the study. Photo courtesy of Zeynel Cebeci via Wikimedia Commons (CC BY-SA 4.0)

These signals, the researchers write, correspond to specific metabolic processes and allow a deeper understanding of how a tree uses C02 throughout its life. What’s more, the researchers found similarities in these isotopic signals within species that could be used to generalize the responses of tree species to changes in atmospheric C02 content and other environmental shifts.

“Our results from 11 trees species show that the 13C / 12C ratios at individual [carbon-hydrogen] positions leave a fingerprint of the regulation of metabolism, which seems to be similar for all species,” said Thomas Wieloch of Sweden’s Umeå University.

Wieloch explained that the metabolic signals his team discovered could be traced back for an entire tree-ring series – potentially thousands of years.

“This study shows that we are able to look into the metabolic history of trees with much higher resolution, so that we possibly can detect if trees acclimate under changing climates,” said Juergen Schleucher, also with Umeå University.

The researchers say the results of their study could be helpful for forest management and climate modeling.

“This newest NMR research results from Umeå could be very relevant to forestry because it could give climate researchers better background facts for their models and give decision-makers new ideas on how to adapt their forest management plans and make estimates of tree production more realistic,” said Schleucher.

Schleucher added that the team will next be looking into the physiological mechanisms behind their newly discovered metabolic signals in the hopes of learning how increasing CO2 concentrations in the atmosphere may influence tree growth over the span of decades.